Reducing leaked downlink interference signals in a remote unit uplink path(s) in a distributed antenna system (DAS)

ABSTRACT

Methods and systems for reducing leaked downlink interference signals in a remote unit uplink path(s) in a distributed antenna system (DAS) are provided. In a remote antenna unit (RAU) disclosed herein, a downlink interference signal may be leaked from a downlink path to an uplink path in the RAU. In this regard, an adjustment circuit is provided in the downlink path of the RAU to suppress the downlink interference signal. A control system is provided in the DAS to monitor the leaked downlink interference signal and control the adjustment circuit in the RAU to minimize the leaked downlink interference signal in the uplink path. By providing the adjustment circuit in the RAU and the control system in the DAS to minimize the leaked downlink interference signal in the uplink path, it is possible to reduce interferences between downlink and uplink communications signals without increasing costs of the RAU.

PRIORITY APPLICATION

This application claims the benefit of priority under 35 U.S.C. § 120 ofU.S. application Ser. No. 14/815,138, filed on Jul. 31, 2015, thecontent of which is relied upon and incorporated herein by reference inits entirety.

BACKGROUND

The disclosure relates generally to distribution of communicationssignals in a distributed antenna system (DAS) and, more particularly, toreducing leaked downlink interference signals in an uplink path(s) inthe DAS resulting from downlink and uplink communications in a remoteunit.

Wireless customers are increasingly demanding digital data services,such as streaming video signals. Concurrently, some wireless customersuse their wireless devices in areas that are poorly serviced byconventional cellular networks, such as inside certain buildings orareas where there is little cellular coverage. One response to theintersection of these two concerns has been the use of DASs. DASs can beparticularly useful when deployed inside buildings or other indoorenvironments where client devices may not otherwise be able toeffectively receive radio frequency (RF) signals from a source. DASsinclude remote antenna units (RAUs) configured to receive and transmitcommunications signals to client devices within the antenna range of theRAUs.

A typical DAS comprises head-end equipment (HEE) communicatively coupledto a plurality of remote units. If the remote units include antennas tosupport transmission and reception of wireless communications signals,the remote units may be referred to as RAUs. The HEE is typicallycommunicatively coupled to a cellular base station. The HEE isconfigured to distribute received downlink communications signals fromthe cellular base station to the RAUs. The RAUs are configured todistribute received uplink communications signals received from clientdevices to the HEE to be provided to the cellular base station. The HEEis configured to receive and support a variety of wirelesscommunications services for distribution to the RAUs, such as widebandcode division multiple access (WCDMA), long term evolution (LTE), andwireless local area network (WLAN) communications services as examples.To distribute the wireless communications services in the DAS, thewireless communications services can be provided in the form of analogRF communications signals and/or digital communications signals to theHEE of the DAS for distribution to the RAUs.

An RAU in the DAS may be configured to support more than one type ofwireless communications service that operates in a variety of RFspectrums and bandwidths. Downlink wireless communications signalsreceived by the RAU are typically amplified by a signal amplifier toincrease signal strength before being distributed to the client devicesthrough one or more coupled antennas. However, the amplified downlinkcommunications signals may include intermodulation products. Forinstance, if two (2) downlink wireless communications signals operatingon an 869 MHz band and an 894 MHz band are amplified by the signalamplifier, intermodulation products may be generated below the 869 MHzband (e.g., 844 MHz, 819 MHz, 794 MHz, and so on) and above the 894 MHzband (e.g., 919 MHz, 944 MHz, 969 MHz, and so on). The intermodulationproducts should be sufficiently isolated to prevent or reduceinterferences on adjacent wireless communication channels.

No admission is made that any reference cited herein constitutes priorart. Applicant expressly reserves the right to challenge the accuracyand pertinency of any cited documents.

SUMMARY

Embodiments of the disclosure relate to reducing leaked downlinkinterference signals in a remote unit uplink path(s) in a distributedantenna system (DAS). In the exemplary DAS disclosed herein, a pluralityof remote units is provided. In a non-limiting example, the plurality ofremote units may be a plurality of remote antenna units (RAUs). Theplurality of RAUs are each configured to receive downlink wirelesscommunications signals in a downlink path and distribute the downlinkcommunications signals to client devices through a coupled antenna. TheRAUs are also each configured to receive uplink communications signalsfrom the client devices through the coupled antenna and distribute theuplink wireless communications signals in an uplink path. At least onedownlink interference signal may be generated when, for example, anon-linear signal amplifier in a RAU amplifies the downlinkcommunications signals in its downlink path. The downlink interferencesignal may be leaked from its downlink path to its uplink path, thusinterfering with the uplink communications signals on the uplink path.In this regard, in one aspect, an adjustment circuit is provided in thedownlink path of at least one RAU in the DAS to suppress a downlinkinterference signal. An interference control system is provided in theDAS outside of the RAUs to monitor the leaked downlink interferencesignal in the uplink path of the at least one RAU and control theadjustment circuit in the at least one RAU to minimize the leakeddownlink interference signal in the uplink path. By providing theinterference control system in the DAS outside of the RAUs to controlthe adjustment circuit(s) in the RAU(s) to minimize leaked downlinkinterference signals in an uplink path of RAU(s) in the DAS,interferences between the downlink communications signals and the uplinkcommunications signals can be reduced without the need to provideinterference control systems in each RAU. Providing an interferencecontrol system in each RAU may increase the cost of the RAU in anundesired manner.

One embodiment of the disclosure relates to a DAS. The DAS comprises ahead-end equipment (HEE) communicatively coupled to a plurality of RAUsover at least one downlink communications medium and at least one uplinkcommunications medium. At least one RAU among the plurality of RAUscomprises a coupling device coupled to a downlink path configured tocarry a downlink signal and an uplink path configured to carry an uplinksignal. The coupling device is configured to receive the downlink signalfrom the downlink path and provide the downlink signal to an antenna.The downlink signal comprises at least one downlink communicationssignal and at least one downlink interference signal. The couplingdevice is also configured to provide the uplink signal to the uplinkpath. The uplink signal comprises an uplink communications signalreceived from the antenna and the at least one downlink interferencesignal leaked from the downlink path to the uplink path. The DAS alsocomprises an interference control system communicatively coupled to theat least one RAU among the plurality of RAUs. The interference controlsystem is configured to provide the at least one downlink communicationssignal to the at least one RAU over the at least one downlinkcommunications medium. The interference control system is alsoconfigured to receive the uplink signal from the at least one RAU overthe at least one uplink communications medium. The interference controlsystem is also configured to measure signal strength of the at least onedownlink interference signal comprised in the uplink signal. Theinterference control system is also configured to generate and providean adjustment control signal to an adjustment circuit in the at leastone RAU to reduce the at least one downlink interference signal in theuplink signal to a minimal level based on the measured signal strengthof the at least one downlink interference signal.

An additional embodiment of the disclosure relates to a method forreducing leaked downlink interference signals in an RAU uplink path in aDAS. The method comprises providing at least one downlink communicationssignal to a downlink path in at least one RAU in a DAS. The method alsocomprises receiving an uplink signal from the at least one RAU. Theuplink signal comprises at least one downlink interference signal leakedfrom the downlink path to an uplink path of the at least one RAU. Themethod also comprises measuring signal strength of at least one downlinkinterference signal comprised in the uplink signal. The method alsocomprises providing an adjustment control signal to the at least one RAUto minimize the at least one downlink interference signal in the uplinksignal based on the measured signal strength of the at least onedownlink interference signal.

An additional embodiment of the disclosure relates to an HEE in a DAS.The HEE comprises a signal generator coupled to at least one RAU among aplurality of RAUs in a DAS over at least one downlink communicationsmedium. The signal generator is configured to generate and distribute atleast one downlink communications signal to a downlink path in the atleast one RAU over the at least one downlink communications medium. TheHEE also comprises a spectrum analyzer coupled to the at least one RAUover at least one uplink communications medium. The spectrum analyzer isconfigured to receive an uplink signal from an uplink path in the atleast one RAU over the at least one uplink communications medium. Theuplink signal comprises at least one downlink interference signal leakedfrom the downlink path to the uplink path in the at least one RAU. Thespectrum analyzer is also configured to measure signal strength of theat least one downlink interference signal comprised in the uplinksignal. The spectrum analyzer is also configured to provide the measuredsignal strength of the at least one downlink interference signal to aprocess controller that is communicatively coupled to the spectrumanalyzer and the signal generator. The process controller is configuredto provide an adjustment control signal to the at least one RAU tominimize the at least one downlink interference signal in the uplinksignal based on the measured signal strength of the at least onedownlink interference signal.

An additional embodiment of the disclosure relates to an RAU in a DAS.The RAU comprises a coupling device coupled to a downlink path and anuplink path. The coupling device is configured to receive a downlinksignal from the downlink path and provide the downlink signal to anantenna. The downlink signal comprises at least one downlinkcommunications signal and at least one downlink interference signal. Thecoupling device is also configured to provide an uplink signal to theuplink path. The uplink signal comprises an uplink communications signalreceived from the antenna and the at least one downlink interferencesignal leaked from the downlink path to the uplink path. The RAU alsocomprises an adjustment circuit comprising a local controllercommunicatively coupled to a process controller in an interferencereduction control system. The local controller is configured to suppressthe at least one downlink interference signal in the downlink signalbased on an adjustment control signal received from the interferencereduction control system that is communicatively coupled to theadjustment circuit.

Additional features and advantages will be set forth in the detaileddescription which follows and, in part, will be readily apparent tothose skilled in the art from the description or recognized bypracticing the embodiments as described in the written description andclaims hereof, as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are merely exemplary and are intendedto provide an overview or framework to understand the nature andcharacter of the claims.

The accompanying drawings are included to provide a furtherunderstanding of the disclosure, and are incorporated in and constitutea part of this specification. The drawings illustrate one or moreembodiments, and together with the description serve to explainprinciples and operation of the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an exemplary distributed antenna system(DAS);

FIG. 2 is a schematic diagram of an exemplary DAS illustrating one RAUamong a plurality of RAUs, wherein at least one downlink interferencesignal in the RAU is leaked by a coupling device from a downlink path toan uplink path;

FIG. 3 is a schematic diagram of an exemplary DAS comprising aninterference control system configured to measure and reduce thedownlink interference signal leaked from the downlink path of the RAU inFIG. 2 to the uplink path of the RAU to a minimal level;

FIG. 4 is a flowchart of an exemplary interference reduction process forreducing the downlink interference signal in the uplink path of the RAUin the DAS in FIG. 3;

FIG. 5 is a schematic diagram of an exemplary HEE, wherein theinterference control system of FIG. 3 may be provided; and

FIG. 6 is a partial schematic cut-away diagram of an exemplary buildinginfrastructure in which the interference control system and anadjustment circuit in the RAU of FIG. 3 can be employed.

DETAILED DESCRIPTION

Embodiments of the disclosure relate to reducing leaked downlinkinterference signals in a remote unit uplink path(s) in a distributedantenna system (DAS). In the exemplary DAS disclosed herein, a pluralityof remote units is provided. In a non-limiting example, the plurality ofremote units may be a plurality of remote antenna units (RAUs). Theplurality of RAUs are each configured to receive downlink wirelesscommunications signals in a downlink path and distribute the downlinkcommunications signals to client devices through a coupled antenna. TheRAUs are also each configured to receive uplink communications signalsfrom the client devices through the coupled antenna and distribute theuplink wireless communications signals in an uplink path. At least onedownlink interference signal may be generated when, for example, anon-linear signal amplifier in a RAU amplifies the downlinkcommunications signals in its downlink path. The downlink interferencesignal may be leaked from its downlink path to its uplink path, thusinterfering with the uplink communications signals on the uplink path.In this regard, in one aspect, an adjustment circuit is provided in thedownlink path of at least one RAU in the DAS to suppress a downlinkinterference signal. An interference control system is provided in theDAS outside of the RAUs to monitor the leaked downlink interferencesignal in the uplink path of the at least one RAU and control theadjustment circuit in the at least one RAU to minimize the leakeddownlink interference signal in the uplink path. By providing theinterference control system in the DAS outside of the RAUs to controlthe adjustment circuit(s) in the RAUs(s) to minimize leaked downlinkinterference signals in an uplink path of RAU(s) in the DAS,interferences between the downlink communications signals and the uplinkcommunications signals can be reduced without the need to provideinterference control systems in each RAU. Providing an interferencecontrol system in each RAU may increase the cost of the RAU in anundesired manner.

Before discussing examples of reducing leaked downlink interferencesignals in an RAU uplink path in a DAS starting at FIG. 2, a discussionof an exemplary DAS that employs a communications medium to supportwireless communications services to a plurality of RAUs that does notinclude reduction of leaked downlink interference signals in RAU uplinkpaths is first provided with reference to FIG. 1.

In this regard, FIG. 1 illustrates distribution of communicationsservices to coverage areas 10(1)-10(N) of a DAS 12, wherein ‘N’ is thenumber of coverage areas. These communications services can includecellular services, wireless services, such as radio frequency (RF)identification (RFID) tracking, Wireless Fidelity (Wi-Fi), local areanetwork (LAN), and wireless LAN (WLAN), and combinations thereof, asexamples. The coverage areas 10(1)-10(N) may be remotely located. Inthis regard, the coverage areas 10(1)-10(N) are created by and centeredon RAUs 14(1)-14(N) connected to a head-end equipment (HEE) 16 (e.g., ahead-end controller, a head-end unit, or a central unit). The HEE 16 maybe communicatively coupled to a signal source 18, for example, a basetransceiver station (BTS) or a baseband unit (BBU). In this regard, theHEE 16 receives downlink communications signals 20D from the signalsource 18 to be distributed to the RAUs 14(1)-14(N). The RAUs14(1)-14(N) are configured to receive the downlink communicationssignals 20D from the HEE 16 over a communications medium 22 to bedistributed to the respective coverage areas 10(1)-10(N) of the RAUs14(1)-14(N). In a non-limiting example, the communications medium 22 maybe a wired communications medium (e.g., a coaxial cable or a category5/6/7 cable), a wireless communications medium, or an opticalfiber-based communications medium. Each of the RAUs 14(1)-14(N) mayinclude an RF transmitter/receiver (not shown) and a respective antenna24(1)-24(N) operably connected to the RF transmitter/receiver towirelessly distribute communications services to client devices 26within the respective coverage areas 10(1)-10(N). The RAUs 14(1)-14(N)are also configured to receive uplink communications signals 20U fromthe client devices 26 in the respective coverage areas 10(1)-10(N) to bedistributed to the signal source 18. The size of a given coverage areaof the coverage areas 10(1)-10(N) is determined by an amount of RF powertransmitted by the respective RAUs 14(1)-14(N), receiver sensitivity,antenna gain, and RF environment, as well as by RF transmitter/receiversensitivity of the client devices 26. The client devices 26 usually havea fixed maximum RF receiver sensitivity, so that the above-mentionedproperties of the RAUs 14(1)-14(N) mainly determine the size of therespective coverage areas 10(1)-10(N).

With continuing reference to FIG. 1, the RF transmitter/receiver in eachof the RAUs 14(1)-14(N) may be connected to the respective antenna24(1)-24(N) through a coupling device (not shown), as opposed toconnecting to the respective antenna 24(1)-24(N) over completelyisolated antenna transmit/receive paths. As such, the coupling device isconfigured to alternate between transmitting the downlink communicationssignals 20D to the respective antenna 24(1)-24(N) and receiving theuplink communications signals 20U from the respective antenna24(1)-24(N). Because the downlink communications signals 20D may beassociated with downlink interference signals (e.g., intermodulationproducts), the downlink interference signals may be leaked by thecoupling device into an uplink path 28, thus degrading the uplinkcommunications signals 20U.

In this regard, FIG. 2 is a schematic diagram of an exemplary DAS 30comprising a plurality of RAUs 32. Only one RAU 32 is shown in FIG. 2,but note that the features of the RAU 32 shown in FIG. 2 can be providedin any of a plurality of RAUs in the DAS 30. In the RAU 32 in FIG. 2, asdiscussed in more detail below, at least one downlink interferencesignal 34 is leaked by a coupling device 36 from a downlink path 38 toan uplink path 40 in the RAU 32. In a non-limiting example, the couplingdevice 36 may be a duplexer, a multiplexer, a hybrid combiner, or acombination thereof. The RAU 32 is communicatively coupled to an HEE 42over at least one downlink communications medium 44 and at least oneuplink communications medium 46. The RAU 32 receives at least onedownlink communications signal 48. In a non-limiting example, thedownlink communications signal 48 may be received from one or moresignal sources (not shown), such as a cellular base station for example.

With continuing reference to FIG. 2, at least one downlink signalamplifier 50 is provided in the downlink path 38 before the couplingdevice 36 to increase signal strength of the downlink communicationssignal 48, which comprises the first downlink signal 48(1) and thesecond downlink signal 48(2) in this example. Due to non-linearities ofthe downlink signal amplifier 50, intermodulation distortion (IMD)products may be generated when the downlink communications signal 48 isamplified. As a result, a downlink signal 52 output by the downlinksignal amplifier 50 may comprise the downlink interference signal 34 inaddition to the downlink communications signal 48. In a non-limitingexample, when the downlink communications signal 48 occupying the 1930MHz-1950 MHz band is amplified by the downlink signal amplifier 50, apair of third order IMD products 34(1) and 34(2) are generated atnineteen hundred and ten megahertz (1910 MHz) and nineteen hundred andseventy megahertz (1970 MHz), respectively. In this regard, the downlinkinterference signal 34 comprises the pair of third order IMD products34(1) and 34(2).

With continuing reference to FIG. 2, the coupling device 36 receives thedownlink signal 52, which comprises the downlink communications signal48 and the downlink interference signal 34, and provides the downlinksignal 52 to an antenna 54 for distribution to one or more clientdevices (not shown). The coupling device 36 also provides an uplinksignal 56, which comprises an uplink communications signal 58 receivedfrom the one or more client devices through the antenna 54, to theuplink path 40 for distribution to the HEE 42 over the uplinkcommunications medium 46. The uplink signal 56 is amplified by an uplinksignal amplifier 59 and then provided to the HEE 42 over the uplinkcommunications medium 46. In a non-limiting example, the uplink signal56 may occupy an eighteen hundred and fifty megahertz (1850 MHz) tonineteen hundred and fifteen megahertz (1915 MHz) band. However, if thecoupling device 36 is unable to sufficiently isolate the downlink path38 from the uplink path 40, the downlink interference signal 34 may beleaked from the downlink path 38 to the uplink path 40. For example, thethird order IMD product 34(1), which occupies the 1910 MHz frequency,will fall into the 1850 MHz-1915 MHz band used by the uplink signal 56,thus degrading the uplink signal 56.

With continuing reference to FIG. 2, one solution for preventing thedownlink interference signal 34 from leaking into the uplink path 40 isto employ high isolation RF filters (e.g., cavity filters) in thecoupling device 36. However, the high isolation RF filters may lead tosignificant cost increase of the RAU 32. Hence, it may be desirable topreserve signal integrity in the uplink path 40 without employing highcost high isolation RF filters in the RAU 32.

In this regard, FIG. 3 is a schematic diagram of an exemplary DAS 60comprising an interference control system 62 configured to measure andreduce the downlink interference signal 34 of FIG. 2 leaked from thedownlink path 38 to the uplink path 40 of at least one RAU 64 in the DAS60 to a minimal level, thus preserving signal integrity in the uplinkpath 40 in the RAU 64. Common elements between FIGS. 2 and 3 are showntherein with common element numbers and thus will not be re-described.

With reference to FIG. 3, the interference control system 62 comprises asignal generator 66, a spectrum analyzer 68, and a process controller70. In a non-limiting example, the process controller 70 may be amicroprocessor, a micro-controller, a field programmable gate array(FPGA), or other circuitry that can be configured to reduce the downlinkinterference signal 34 leaked from the downlink path 38 to the uplinkpath 40 of the RAU 64. The signal generator 66 is communicativelycoupled to the RAU 64 over the downlink communications medium 44. Thespectrum analyzer 68 is communicatively coupled to the RAU 64 over theuplink communications medium 46. Additionally, the signal generator 66,the spectrum analyzer 68, and the process controller 70 may becommunicatively coupled by an internal communication link 72. As will bediscussed in more detail below, the signal generator 66 is configured toprovide the downlink communications signal 48 to the RAU 64, and thespectrum analyzer 68 is configured to measure the downlink interferencesignal 34 in the uplink signal 56.

With continuing reference to FIG. 3, the RAU 64 comprises a firstdownlink signal amplifier 74 and a second downlink signal amplifier 76disposed according to a serial arrangement in the downlink path 38before the coupling device 36. The first downlink signal amplifier 74and the second downlink signal amplifier 76 are provided in the RAU 64to ensure that the downlink signal 52 is amplified adequately to desiredsignal strength. The RAU 64 also comprises an adjustment circuit 78. Theadjustment circuit 78 comprises a local controller 80 and an adjustablematching circuit 82. The local controller 80 is configured to becontrolled by the process controller 70 to improve linearity of thefirst downlink signal amplifier 74 and thus, reduce the downlinkinterference signal 34. The local controller 80 may be a microprocessor,micro-controller, field programmable gate array (FPGA), or othercircuitry that can be configured to reduce the downlink interferencesignal 34. The local controller 80 is communicatively coupled to theprocess controller 70 in the interference control system 62 by acommunication link 84. In a non-limiting example, the communication link84 may be a dedicated serial communication cable or a dedicated Ethernetcommunication cable. In another non-limiting example, the communicationlink 84 may be provided over the downlink communications medium 44.

With continuing reference to FIG. 3, the adjustable matching circuit 82is disposed between the first downlink signal amplifier 74 and thesecond downlink signal amplifier 76. According to previous discussionsregarding FIG. 2, when the downlink communications signal 48 isamplified, the downlink interference signal 34 may be generated in thedownlink signal 52 due to non-linearities of the first downlink signalamplifier 74 and the second downlink signal amplifier 76. In thisregard, by disposing the adjustable matching circuit 82 after the firstdownlink signal amplifier 74, it is possible to improve the linearity ofthe first downlink signal amplifier 74, thus suppressing the downlinkinterference signal 34 in the downlink signal 52. Further, by disposingthe adjustable matching circuit 82 before the second downlink signalamplifier 76, it is possible to compensate for insertion loss introducedby the adjustable matching circuit 82 to ensure that the downlink signal52 is amplified adequately to the desired signal strength.

With continuing reference to FIG. 3, in a non-limiting example, theadjustable matching circuit 82 may be an LC matching circuit. Theadjustable matching circuit 82 comprises a capacitor circuit 86. Thecapacitor circuit 86 comprises a capacitor 88 and an adjustablecapacitor 90 disposed according to a parallel arrangement. Theadjustable capacitor 90 comprises a plurality of capacitance values. Ina non-limiting example, the adjustable capacitor 90 may be set tothirty-two (32) different capacitance values. As such, by setting theadjustable capacitor 90 to a capacitance value among the plurality ofcapacitance values, it is possible to change the capacitance value ofthe adjustable matching circuit 82. The adjustable matching circuit 82also comprises an inductor 92, which has a first end 94 coupled to thefirst downlink signal amplifier 74 before the capacitor circuit 86 and asecond end 96 coupled to a ground 98. The capacitor circuit 86 and theinductor 92 are used to obtain a conjugate impedance match with thefirst downlink signal amplifier 74, thus improving the linearity of thefirst downlink signal amplifier 74. In this regard, it is possible tocontrol the adjustable matching circuit 82 by adjusting the adjustablecapacitor 90 to minimize the downlink interference signal 34 in thedownlink path 38, therefore reducing the downlink interference signal 34leaked into the uplink path 40.

With continuing reference to FIG. 3, the RAU 64 also comprises a switch100 that is disposed between the coupling device 36 and the antenna 54.The local controller 80 may control the switch 100 to couple thecoupling device 36 to the antenna 54 or decouple the coupling device 36from the antenna 54 by providing a switch control signal 102 to theswitch 100. When the coupling device 36 is coupled to the antenna 54 bythe switch 100, the RAU 64 is in an operating mode operation. Incontrast, when the coupling device 36 is decoupled from the antenna 54by the switch 100, the RAU 64 is in a commissioning mode operation. In anon-limiting example, the coupling device 36 may be coupled to theground 98 by a resistor 104. In another non-limiting example, theresistor 104 has a resistance of fifty ohms (50Ω). When the RAU 64 is inthe commissioning mode operation, the RAU 64 will not be able to receivethe uplink communications signal 58 from the one or more client devicesas the antenna 54 is decoupled. As such, the uplink signal 56 will onlyinclude the downlink interference signal 34 leaked from the downlinkpath 38 by the coupling device 36.

In this regard, to minimize the downlink interference signal 34 leakedinto the uplink path 40 of the RAU 64, the process controller 70 in theinterference control system 62 first configures the RAU 64 for thecommissioning mode operation by providing an adjustment control signal106 to the local controller 80 in the RAU 64 over the communication link84. In a non-limiting example, the adjustment control signal 106 isindicative of matching circuit adjustment. In response to receiving theadjustment control signal 106 indicative of matching circuit adjustment,the local controller 80 provides the switch control signal 102 to theswitch 100 to decouple the coupling device 36 from the antenna 54, thusconfiguring the RAU 64 for the commissioning mode operation. Next, theprocess controller 70 uses the internal communication link 72 toinstruct the signal generator 66 to provide the downlink communicationssignal 48 to the downlink path 38 of the RAU 64 over the downlinkcommunications medium 44. In a non-limiting example, the downlinkcommunications signal 48 may be a test signal that occupies the same1930 MHz-1950 MHz band as the downlink communications signal 48 occupieswhen the RAU 64 is in the operating mode operation.

With continuing reference to FIG. 3, the spectrum analyzer 68 in theinterference control system 62 receives the uplink signal 56 over theuplink communications medium 46. As mentioned above, the uplink signal56 now only includes the downlink interference signal 34 leaked from thedownlink path 38 because the RAU 64 has been configured for thecommissioning mode operation. The spectrum analyzer 68 measures thesignal strength of the downlink interference signal 34 received from theRAU 64 and provides the measured signal strength to the processcontroller 70 over the internal communication link 72.

The process controller 70 receives the measured signal strength of thedownlink interference signal 34 from the spectrum analyzer 68. If themeasured signal strength indicates that the downlink interference signal34 is not minimized, the process controller 70 provides the adjustmentcontrol signal 106 indicative of matching circuit adjustment to thelocal controller 80. In response to receiving the adjustment controlsignal 106 indicative of matching circuit adjustment, the localcontroller 80 sets the adjustable capacitor 90 to a capacitance value,which is selected from the plurality of capacitance values of theadjustable capacitor 90 and is different from a present capacitancevalue of the adjustable capacitor 90. By setting the adjustablecapacitor 90 to a different capacitance value, the linearity of thefirst downlink signal amplifier 74 is changed. Hence, another signalstrength measurement of the downlink interference signal 34 can be takenby the spectrum analyzer 68 and provided to the process controller 70.In a non-limiting example, it is possible for the local controller 80 tosweep all of the plurality of capacitance values of the adjustablecapacitor 90 to minimize the downlink interference signal 34.

In a non-limiting example, if the measured signal strength indicatesthat the downlink interference signal 34 is minimized, the processcontroller 70 provides the adjustment control signal 106 indicative ofmatching circuit settlement to the local controller 80. In response toreceiving the adjustment control signal 106 indicative of matchingcircuit settlement, the local controller 80 stores the presentcapacitance value of the adjustable capacitor 90 as a preferredcapacitance value in a local storage media 107. In a non-limitingexample, the local storage media 107 may be Non-volatile Random AccessMemory (NVRAM), Universal Flash Storage (UFS), embedded Multimedia Card(eMMC), and so on. The local controller 80 then provides the switchcontrol signal 102 to the switch 100 to configure the RAU 64 for theoperating mode operation based on the preferred capacitance value storedin the local storage media 107. Hence, by repeatedly adjusting thecapacitance value of the adjustable capacitor 90 based on the measuredsignal strength of the downlink interference signal 34, it is possibleto minimize the downlink interference signal 34 in the uplink path 40 ofthe RAU 64.

With continuing reference to FIG. 3, in a non-limiting example, thedownlink communications medium 44 may be at least one opticalfiber-based downlink communications medium 44(1). Likewise, the uplinkcommunications medium 46 may be at least one optical fiber-based uplinkcommunications medium 46(1). In this regard, an electrical-to-optical(E/O) converter 108 is disposed between the signal generator 66 and theoptical fiber-based downlink communications medium 44(1). Likewise, anoptical-to-electrical (O/E) converter 110 is disposed between thespectrum analyzer 68 and the optical fiber-based uplink communicationsmedium 46(1). The E/O converter 108 converts the downlink communicationssignal 48 to an optical downlink communications signal 112 fordistribution to the RAU 64. The RAU 64 comprises a second O/E converter114 for converting the optical downlink communications signal 112 backto the downlink communications signal 48. The RAU 64 also comprises asecond E/O converter 116 for converting the uplink signal 56 to anoptical uplink signal 118 for distribution to the interference controlsystem 62. The O/E converter 110 in the interference control system 62subsequently converts the optical uplink signal 118 back to the uplinksignal 56. In a non-limiting example, the optical fiber-based downlinkcommunications medium 44(1) and the optical fiber-based uplinkcommunications medium 46(1) may be provided as a single optical fiber.In this regard, the optical downlink communications signal 112 and theoptical uplink signal 118 may be communicated over the single opticalfiber via wavelength division multiplexing (WDM).

FIG. 4 is a flowchart of an exemplary interference reduction process 120for reducing the downlink interference signal 34 in the uplink path 40of the RAU 64 of FIG. 3.

With reference to FIG. 4, prior to starting the interference reductionprocess 120, the interference control system 62 may optionally configurethe RAU 64 for the commissioning mode operation. The interferencecontrol system 62 provides the downlink communications signal 48 to thedownlink path 38 in the RAU 64 of the DAS 60 (block 122). Next, theinterference control system 62 receives the uplink signal 56, whichcomprises the downlink interference signal 34 leaked from the downlinkpath 38 to the uplink path 40, from the RAU 64 (block 124). Theinterference control system 62 then measures the signal strength of thedownlink interference signal 34 comprised in the uplink signal 56 (block126). Subsequently, the interference control system 62 provides theadjustment control signal 106 to the RAU 64 to minimize the downlinkinterference signal 34 in the uplink signal 56 based on the measuredsignal strength of the downlink interference signal 34 (block 128). Oncethe downlink interference signal 34 is minimized, the interferencecontrol system 62 may configure the RAU 64 for the operating modeoperation.

With reference back to FIG. 3, the interference control system 62 isprovided outside of the RAU 64. In this regard, the interference controlsystem 62 may be configured flexibly to measure and reduce the downlinkinterference signal 34 in any RAU (not shown) in the DAS 60 to theminimal level. In a non-limiting example, the interference controlsystem 62 of FIG. 3 may be provided in an HEE, or any intermediateequipment located between the HEE and the RAU 64, in the DAS 60. In thisregard, FIG. 5 is a schematic diagram of an exemplary HEE 130, whereinthe interference control system 62 of FIG. 3 may be provided. Commonelements between FIGS. 3 and 5 are shown therein with common elementnumbers and will not be re-described herein.

With reference to FIG. 5, the HEE 130 comprises a radio interface module(RIM) 132 and an optical interface module (OIM) 134. The OIM 134 maycomprise the E/O converter 108 (not shown) and the O/E converter 110(not shown) of FIG. 3. In a first non-limiting example, the spectrumanalyzer 68 may be provided between the RIM 132 and the OIM 134. In asecond non-limiting example, the spectrum analyzer 68 may be providedinside the RIM 132. In a third non-limiting example, the signalgenerator 66 may be provided inside the RIM 132. In a fourthnon-limiting example, the process controller 70 may be provided insidethe HEE 130.

The interference control system 62 and the adjustment circuit 78 of FIG.3 may be provided in an indoor environment, as illustrated in FIG. 6.FIG. 6 is a partial schematic cut-away diagram of an exemplary buildinginfrastructure 140 in which the interference control system 62 and theadjustment circuit 78 of FIG. 3 can be employed. The buildinginfrastructure 140 in this embodiment includes a first (ground) floor142(1), a second floor 142(2), and a third floor 142(3). The floors142(1)-142(3) are serviced by a central unit 144 to provide antennacoverage areas 146 in the building infrastructure 140. In a non-limitingexample, the interference control system 62 may be provided in thecentral unit 144. The central unit 144 is communicatively coupled to abase station 148 to receive downlink communications signals 150D fromthe base station 148. The central unit 144 is communicatively coupled toRAUs 152 to receive uplink communications signals 150U from the RAUs152, as previously discussed above. The downlink communications signals150D and the uplink communications signals 150U communicated between thecentral unit 144 and the RAUs 152 are carried over a riser cable 154. Inanother non-limiting example, the adjustment circuit 78 may be providedin the RAUs 152. The riser cable 154 may be routed through interconnectunits (ICUs) 156(1)-156(3) dedicated to each of the floors 142(1)-142(3)that route the downlink communications signals 150D and the uplinkcommunications signals 150U to the RAUs 152 and also provide power tothe RAUs 152 via array cables 158.

Unless otherwise expressly stated, it is in no way intended that anymethod set forth herein be construed as requiring that its steps beperformed in a specific order. Accordingly, where a method claim doesnot actually recite an order to be followed by its steps or it is nototherwise specifically stated in the claims or descriptions that thesteps are to be limited to a specific order, it is in no way intendedthat any particular order be inferred.

It will be apparent to those skilled in the art that variousmodifications and variations can be made without departing from thespirit or scope of the invention. Since modifications, combinations,sub-combinations, and variations of the disclosed embodimentsincorporating the spirit and substance of the invention may occur topersons skilled in the art, the invention should be construed to includeeverything within the scope of the appended claims and theirequivalents.

What is claimed is:
 1. A wireless communication system, comprising: aplurality of remote units located on multiple floors of aninfrastructure, each remote unit configured to receive opticalcommunications signals and having at least one antenna; a head-endequipment (HEE) communicatively coupled to the plurality of remote unitsover at least one downlink optical communications medium and at leastone uplink optical communications medium; wherein at least one remoteunit among the plurality of remote units comprises a coupling devicecoupled to a downlink path configured to carry a downlink signal and anuplink path configured to carry an uplink signal, the coupling deviceconfigured to: receive the downlink signal from the downlink path andprovide the downlink signal to an antenna, wherein the downlink signalcomprises at least one downlink communications signal and at least onedownlink interference signal; and provide the uplink signal to theuplink path, wherein the uplink signal comprises an uplinkcommunications signal received from the antenna and the at least onedownlink interference signal leaked from the downlink path to the uplinkpath; and an interference control system communicatively coupled to theat least one remote unit among the plurality of remote units, theinterference control system configured to: provide the at least onedownlink communications signal to the at least one remote unit over theat least one downlink optical communications medium; receive the uplinksignal from the at least one remote unit over the at least one uplinkoptical communications medium; measure signal strength of the at leastone downlink interference signal comprised in the uplink signal; andgenerate and provide an adjustment control signal to an adjustmentcircuit in the at least one remote unit to reduce the at least onedownlink interference signal in the uplink signal.
 2. The wirelesscommunication system of claim 1, wherein the adjustment circuitcomprises a local controller configured to suppress the at least onedownlink interference signal in the downlink signal based on theadjustment control signal.
 3. The wireless communication system of claim2, wherein the interference control system comprises: a signal generatorconfigured to generate and distribute the at least one downlinkcommunications signal to the at least one remote unit over the at leastone downlink optical communications medium; and a spectrum analyzerconfigured to: receive the uplink signal from the at least one remoteunit over the at least one uplink optical communications medium; andmeasure the signal strength of the at least one downlink interferencesignal comprised in the uplink signal.
 4. The wireless communicationsystem of claim 2, wherein the interference control system furthercomprises: a process controller communicatively coupled to the signalgenerator, the spectrum analyzer, and the adjustment circuit in the atleast one remote unit, the process controller configured to: configurethe at least one remote unit for a commissioning mode operation byproviding an adjustment control signal indicative of matching circuitadjustment; instruct the signal generator to provide the downlink signalto the at least one remote unit; receive the measured signal strength ofthe at least one downlink interference signal from the spectrumanalyzer; provide the adjustment control signal indicative of matchingcircuit adjustment if the measured signal strength indicates that the atleast one downlink interference signal is not minimized; and provide anadjustment control signal indicative of matching circuit settlement ifthe measured signal strength indicates that the at least one downlinkinterference signal is minimized.
 5. The wireless communication systemof claim 4, wherein the process controller is communicatively coupled tothe adjustment circuit in the at least one remote unit over a dedicatedserial communication cable.
 6. The wireless communication system ofclaim 4, wherein the process controller is communicatively coupled tothe adjustment circuit in the at least one remote unit over a dedicatedEthernet communication cable.
 7. The wireless communication system ofclaim 4, wherein the process controller is communicatively coupled tothe adjustment circuit in the at least one remote unit over the at leastone downlink optical communications medium.
 8. The wirelesscommunication system of claim 4, wherein the at least one remote unitamong the plurality of remote units further comprises a first downlinksignal amplifier and a second downlink signal amplifier disposed in aserial arrangement in the downlink path.
 9. The wireless communicationsystem of claim 8, wherein the adjustment circuit in the at least oneremote unit comprises an adjustable matching circuit disposed betweenthe first downlink signal amplifier and the second downlink signalamplifier, the adjustable matching circuit comprising: a capacitorcircuit disposed between the first downlink signal amplifier and thesecond downlink signal amplifier, the capacitor circuit comprising acapacitor and an adjustable capacitor disposed in a parallelarrangement; and an inductor comprising a first end coupled to the firstdownlink signal amplifier before the capacitor circuit and a second endcoupled to a ground.
 10. The wireless communication system of claim 9,wherein the local controller is communicatively coupled to the processcontroller in the interference control system, the local controllerconfigured to: set the adjustable capacitor to a capacitance value amonga plurality of capacitance values of the adjustable capacitor inresponse to receiving the adjustment control signal indicative ofmatching circuit adjustment, wherein the capacitance value is differentfrom a present capacitance value of the adjustable capacitor; and storethe present capacitance value of the adjustable capacitor as a preferredcapacitance value in a local storage media in response to receiving theadjustment control signal indicative of matching circuit settlement. 11.The wireless communication system of claim 10, wherein the at least oneremote unit further comprises a switch disposed between the couplingdevice and the antenna, the switch configured to be controlled by thelocal controller to couple the coupling device to the antenna ordecouple the coupling device from the antenna.
 12. The wirelesscommunication system of claim 4, wherein the local controller is furtherconfigured to configure the at least one remote unit for thecommissioning mode operation in response to receiving the adjustmentcontrol signal indicative of matching circuit adjustment by controllinga switch to decouple the coupling device from the antenna.
 13. Thewireless communication system of claim 4, wherein the local controlleris further configured to configure the at least one remote unit for anoperating mode operation in response to receiving the adjustment controlsignal indicative of matching circuit settlement by controlling a switchto couple the coupling device to the antenna.
 14. A wirelesscommunication system, comprising: a plurality of remote unitsdistributed throughout an infrastructure, each remote unit configured toreceive optical communications signals and having at least one antenna;and a head-end equipment (HEE) communicatively coupled to the remoteunits and comprising: a signal generator coupled to at least one of theremote units over at least one downlink optical communications medium,the signal generator configured to generate and distribute at least onedownlink communications signal to a downlink path in the at least oneremoute unit over the at least one downlink optical communicationsmedium; and a spectrum analyzer coupled to the at least one remote unitover at least one uplink optical communications medium, the spectrumanalyzer configured to: receive an uplink signal from an uplink path inthe at least one remote unit over the at least one uplink opticalcommunications medium, wherein the uplink signal comprises at least onedownlink interference signal leaked from the downlink path to the uplinkpath in the at least one remote unit; measure signal strength of the atleast one downlink interference signal comprised in the uplink signal;and provide the measured signal strength of the at least one downlinkinterference signal to a process controller that is communicativelycoupled to the spectrum analyzer and the signal generator; and whereinthe process controller is configured to provide an adjustment controlsignal to the at least one remote to minimize the at least one downlinkinterference signal in the uplink signal based at least in part on themeasured signal strength of the at least one downlink interferencesignal.
 15. The wireless communication system of claim 14, wherein theprocess controller is configured to provide the adjustment controlsignal to the at least one remote unit over a dedicated serialcommunication cable.
 16. The wireless communication system of claim 14,wherein the process controller is configured to provide the adjustmentcontrol signal to the at least one remote unit over a dedicated Ethernetcommunication cable.
 17. The wireless communication system of claim 14,wherein the process controller is configured to provide the adjustmentcontrol signal to the at least one remote unit over the at least onedownlink optical communications medium.
 18. The wireless communicationsystem of claim 14, further comprising: an electrical-to-optical (E/O)converter configured to convert the at least one downlink communicationssignal to an optical downlink communications signal; and anoptical-to-electrical (O/E) converter configured to convert an opticaluplink signal into the uplink signal.